This invention is generally directed to molecularly dispersed pigments, the preparation of thin films containing molecularly dispersed pigments, and to imaging members thereof. More specifically, the present invention is directed to processes employing Lewis acid-pigment solubilization for fabricating solution coated photosensitive pigment layers, and photo- and opto-electronic devices and imaging members thereof. In embodiments of the present invention, there are provided layered photoconductive imaging members with improved xerographic properties, inclusive of high charge acceptance, low dark decay, high photosensitivity in the wavelength regions of from about 400 to about 900 nanometers, and maximum or peak photosensitivity in the wavelength regions of from about 600 to about 800 nanometers, enabling their selection for electrophotographic, especially xerographic, imaging systems and printers sensitive to near infrared wavelengths. In embodiments of the invention of the present application, there are provided imaging members with photoconductive layers comprised of molecularly dispersed pigments illustrated herein, and charge or hole transport layers, especially those comprised of aryl amines, which members are sensitive to light in the wavelength region of from about 700 to about 820 nanometers. The resulting members are responsive to red illumination originating from light emitting diode (LED) printing apparatuses. Imaging members prepared by processes of the present invention can be used in, or in conjunction with, optoelectronic devices such as light emitting diodes, organic electroluminescent emitters, field effect transistors, vacuum fluorescent displays, thin film transistors, and liquid crystal displays. The photoresponsive imaging members of the present invention can contain, for example, situated between a photogenerating layer and a charge transporting layer, or situated between a photogenerating layer and a supporting substrate with a charge transport layer in contact with the photogenerating layer, a photoconductive composition comprised of the molecularly dispersed photogenerating pigments as illustrated herein.
In embodiments of the present invention, there are provided alternative and simplified processes, dissimilar than traditional high energy pigment attrition and high vacuum pigment sublimation processes, for the fabrication of pigment containing photosensitive layered devices. Known pigment attrition processes involves reduction of pigment particle size by high energy grinding or attrition typically conducted in a dispersion medium. The resulting pigment dispersion is then used to cast pigmented layers on selected substrates by, for example, spray, dip, spin, and the like, coating techniques. Although fine pigment particles can be obtained by prolonged attrition processing, the resulting pigment dispersions often reagglomerate in time. A wide variety of pigment dispersants have been employed to avoid rapid aggregate formation with different varying degrees of success. A binder resin, which may be solubilized in the molecular pigment dispersion and/or precoated onto the substrates, is optionally used to provide necessary mechanical strength for the deposited pigment layer or layers. Pigment sublimation processes involve heating pigment particles under high vacuum to vaporize the pigment molecules which are then condensed onto cooled substrates to form a pigment layer. Pure pigment layers with high degree of uniformity are achievable by the sublimation process. However, sublimation processing may be a complicated and expensive proposition for large scale production operations. Processes are also known for the preparation and purification of photosensitive pigments involving sequential dissolution and reprecipitation of the pigment using, for example, an organic or inorganic acid solvent system followed by a non solvent system as disclosed, for example, in U.S. Pat. Nos. 5, 153,094 and 5,153,313. However, the pigment solutions disclosed in these patents have not been used directly in the preparation of photogenerating layers. Major disadvantages of using strong acid solvent solutions for larger scale production of films of photoconductive pigments include the highly corrosive and toxic nature of the acidic solvents; and acid solvents are generally not sufficiently volatile and are difficult to remove from the films.
In embodiments of the present invention, there are provided imaging members with a photoconductive layer comprised of the molecularly dispersed pigments as illustrated herein, that is, an imaging member with a layer that functions simultaneously both as charge generating layer and transport layer.
Certain layered imaging members are known, including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990; and overcoated photoresponsive materials containing a hole injecting layer overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer; and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers include certain diamines as mentioned therein.
The following United States patents are mentioned: 4,299,896 which discloses imaging members with a photosensitive layer selected from the disazo pigments of the formulas illustrated, for example, in the Abstract, and in column 2; 4,314,015 wherein the disazo pigments for the imaging member are of the formula as illustrated in the Abstract, for example, and column 2; 4,666,810 wherein the azo pigments are illustrated in column 2 for example; and 4,797,337 wherein the disazo photogenerating pigment is of the formula as illustrated in the Abstract, for example, which disazos may contain a SO.sub.2 group.
U.S. Pat. No. 4,713,307, discloses photoconductive imaging members containing a supporting substrate, certain azo pigments as photogenerating materials, and a hole transport layer that preferably contains an aryl diamine compound dispersed in an inactive resinous binder.
U.S. Pat. No. 4,797,337, discloses a photoconductive imaging member comprising a supporting substrate, a hole transport layer, and a photogenerating layer comprising specific disazo compounds.
Additional references illustrating layered organic electrophotographic photoconductor elements with azo, bisazo, and related compounds include U.S. Pat. No. 4,390,611, U.S. Pat. No. 4,551,404, U.S. Pat. No. 4,596,754, Japanese Patent 60-64354, U.S. Pat. No. 4,400,455, U.S. Pat. No. 4,390,608, U.S. Pat. No. 4,327,168, U.S. Pat. No. 4,299,896, U.S. Pat. No. 4,314,015, U.S. Pat. No. 4,486,522, U.S. Pat. No. 4,486,519, U.S. Pat. No. 4,555,667, U.S. Pat. No. 4,440,845, U.S. Pat. No. 4,486,800, U.S. Pat. No. 4,309,611, U.S. Pat. No. 4,418,133, U.S. Pat. No. 4,293,628, U.S. Pat. No. 4,427,753, U.S. Pat. No. 4,495,264, U.S. Pat. No. 4,359,513, U.S. Pat. No. 3,898,084, U.S. Pat. No. 4,830,944, U.S. Pat. No. 4,820,602, and Japanese Patent Publication 60-111247.
U.S. Pat. No. 4,755,443 discloses a photoreceptor for electrophotography which comprises a charge carrier generating material and charge transport material wherein one charge generating material is a metal phthalocyanine or a metal-free phthalocyanine. The layer containing the generator material also contains an organic amine. Other carrier generating substances can be used in combination with the phthalocyanine generator material, including azo pigments, anthraquinone dyes, perylene dyes, polycyclic quinone dyes, and methine stearate pigments.
U.S. Pat. No. 4,424,266 discloses an electrophotographic photosensitive element having a conductive support and a photosensitive layer comprising a carrier generating phase layer containing a carrier generating material selected from the group consisting of perylene dyes, polycyclic quinones, and azo dyes, and a carrier transporting phase layer containing a hydrazone carrier transporting material. The carrier generator materials can be used either singly or in combination.
U.S. Pat. No. 4,882,254, discloses a layered photoresponsive imaging member which comprises a supporting substrate, a photogenerator layer comprising a mixture of first and second pigments, and an aryl amine hole transport layer. The mixture of pigments is selected from perylenes and phthalocyanines, polycyclic quinones and phthalocyanines, or perinones and phthalocyanines.
Photoresponsive imaging members containing perinone and perylene compounds are also known. For example, European Patent Publication 0040402, DE3019326, filed May 21, 1980, discloses the use of N,N'-disubstituted perylene-3,4,9,10-tetracarboxyldiimide pigments as photoconductive substances.
Imaging members with phthalocyanine materials are also known as disclosed in, for example, U.S. Pat. No. 3,594,163, U.S. Pat. No. 3,657,272, U.S. Pat. No. 3,816,118, U.S. Pat. No. 3,862,127, U.S. Pat. No. 3,903,107, U.S. Pat. No. 3,927,026, U.S. Pat. No. 3,932,180, U.S. Pat. No. 3,932,454, U.S. Pat. No. 4,031,109, U.S. Pat. No. 4,098,795, and U.S. Patent Re. 27,117.
Processes for preparing imaging members by dispersion or suspension methodology are disclosed in U.S. Pat. Nos. 4,514,482, 4,555,463 and 4,587,189.
The disclosures of each of the above mentioned patents and publications are totally incorporated herein by reference.
Imaging members and processes thereof are illustrated in copending applications U.S. Ser. No. 08/011,590 (D/92578, Abkowitz) filed Feb. 1, 1993, and U.S. Ser. No. 07/844,085 (D/91668), filed Mar. 2, 1992, the disclosures of which are totally incorporated herein by reference.